The aim of the work: The aim of this work is to evaluate the role of exercise and / or irisin in cases of hypothyroid male rats Material and Methods: 90 local strain male rats divided into two groups: Group 1-Without exercise which is divided five subgroups 10 rats each, Subgroup Ia Euthyroid Control rats receive 0.5 ml physiological saline daily intraperitoneal (IP) for 3 weeks. Subgroup. IIa Hypothyroid Control rats will be injected by 6-n-propyl-2thiouracil (PTU) with a dose 10 mg/kg/day (IP) for 3 weeks. subgroup IIIa L-Thyroxine Treated Hypothyroid rats: Induction of hypothyroid as in group IIa then will receive L-Thyroxine hormone (IP) with a dose of 1.5mg /kg/day for 10 days. Subgroup VIa Irisin Treated Hypothyroid rats: Induction of hypothyroid as in subgroup IIa then will receive Irisin hormone (IP) with a dose of 10?g/kg/day for 10 days. subgroup Va Irisin & L-Thyroxine treated hypothyroid rats Induction of hypothyroid as in subgroup 2a then will receive Irisin hormone as in subgroup 4a and L-Thyroxine as in subgroup 3a for 10 days. Group 2-With Acute Forced Swimming which is divided into five subgroups 10 rats each Subgroup Ib: Euthyroid Control Acute Forced Swimming subgroup: will be treated as subgroup 1a then will be submitted to acute forced swimming .Subgroup II b: Hypothyroid Acute Forced Swimming treated as in subgroup IIa then will be submitted to acute forced swimming. Subgroup III b: Thyroxine treated hypothyroid acute forced swimming subgroup: treated as in subgroup II a, then will be submitted to acute forced swimming then will receive L-Thyroxine as in subgroup IIIa. Subgroup IV b: Irisin treated hypothyroid acute forced swimming group: treated as subgroup II a, then will be submitted to acute forced swimming then will receive Irisin similar to subgroup IVa. For all these rats, For group 2, the Maximal Swimming Time (MST) were measured then for all animal studied the body weight, body mass index and abdominal circumference were measured one day before and at the end of experimental period. Tri-iodithyronine (T3), Thyroxin (T4), Thyroid Stimulating Hormone (TSH), Irisin and Creatin Kinase (CK) were measured also lipid profile will be measured Triglycerides, cholesterol, LDL, HDL and phospholipids. Results: In hypothyroid rats, irisin injection only caused decrease in body weight, abdominal circumference and body mass index with decrease in lipid profile but no improvement in thyroid function tests. While L-thyroxine injection only caused improvement in thyroid function tests but no significant improvement in anthropometric measurements and lipid profile. On the other hand, injection of both irisin and L-thyroxine gave the best results in all parameters as both improved anthropometric measurements, lipid profile and thyroid function tests. hypothyroid animal had significant increase in serum CK levels as compared to normal euthyroid rats. L-thyroxine when given as treatment to hypothyroid rats caused significant reduction in CK However, when irisin was given as a treatment to hypothyroid animals, it caused more increase in irisin than hypothyroid rats Acute exercise causes significant decrease in MST in hypothyroid animals and those treated with irisin as compared to control and those of hypothyroid treated with thyroxine However Acute exercise caused no significant change in all other parameters studied Conclusion: Irisin has a major role in reducing weight by converting white fat tissue into brown adipose tissue and then to heat. On the other side of the study, irisin has no direct effect on improving the secretion of thyroid hormones in people with thyroid hormone deficiency. Also, the injectable exogenous irisin has a better and more potent effect than the endogenous irisin resulting from acute short-term exercise.